The following abbreviations are herewith defined, at least some of which are referred to within the following description of the state-of-the-art and the present invention.    APON ATM PON    ATM Asynchronous Transfer Mode    CO Central Office    EPON Ethernet PON    GPON Gigabit PON    IEEE Institute of Electrical and Electronics Engineers    ITU International Telecommunication Union    OLT Optical Line Terminal    ONT Optical Network Terminal    ONU Optical Network Terminal    PON Passive Optical Network    TDMA Time Division Multiple Access
Passive optical network (PON) is a widely used technology for residential and business broadband access. PONs are considered to be inexpensive for network operators because they do not require any active equipment or power supplies between the operator's central office (CO) and customer's premises (CP). PON traffic flows between the Optical Line Terminal (OLT) residing in the CO towards a number of Optical Network Terminals (ONT) or Optical Network Terminals (ONU), residing on the CP.
The OLT is the only unit transmitting in the downstream direction. The upstream PON traffic shares the same optical fiber with the downstream traffic, utilizing a different wavelength and is driven by all ONTs. In order to prevent collisions that may occur if two or more ONTs are transmitting simultaneously, upstream PON traffic is managed in the Time Division Multiple Access (TDMA) fashion. One of the functions of the OLT is to schedule and grant separate time slots to each ONT, thus avoiding collision between upstream packets. Transmitter lasers (or other light sources) of each ONT can be turned on only during their respective transmission time slots. The OLT must be capable of receiving bursts of data from different ONTs.
The evolution of the PON systems and standards has seen a steady increase in PON bit rate ranging from the initial 155 Mb/s in APON, to 1.25 Gb/s in Gigabit-capable PON (GPON) as specified in ITU-T G.984 and Ethernet PON (EPON) as specified in IEEE 802.3ah, up to 10 Gb/s currently specified in the IEEE 802.3av (10GEPON) and ITU-T 10G GPON standards. The high bit rates result in increased energy consumption in both the OLT and ONT, posing a challenges for the implementation of central office equipment including cooling issues caused by increased power dissipation and operational expenses incurred by increasing electrical energy consumption.
Note that the techniques or schemes described herein as existing or possible are presented as background for the present invention, but no admission is made thereby that these techniques and schemes were heretofore commercialized or known to others besides the inventors.
Accordingly, there has been and still is a need to address the aforementioned shortcomings and other shortcomings associated with energy use in optical networks. These needs and other needs are satisfied by the present invention.